I have written an article about how to customize the Ubuntu login screen. After you edit the login screen, you may want to share your work on blogs and forums. However, you simply cannot just press the print-screen button to take screenshot of the login screen in Ubuntu. To do so, you can use a workaround command to preview the login screen and take screenshot of it. Just open the terminal and run the following command:

unity-greeter --test-mode

And you will have a preview of the login screen of Ubuntu, you can also select the sessions to see the background of the login screen for each session:

How to take screenshot of the login screen of Linux Mint 13

If you use Linux Mint, the above method doesnt work. To take screenshot of the MDM login screen of Linux Mint 13 (both MATE and Cinnamon editions), you can edit the file /etc/mdm/Init/Default. Just use a text editor to open this file as root, in MATE edition, the command will be:

sudo pluma /etc/mdm/Init/Default

Just scroll through the whole file and append a command to take screenshot after a delay right above the last line. You can use whatever screenshot tool you like. In MATE, the default screenshot tool is mate-screenshot so the command you can use will be (I use the delay of 5 seconds here):

( mate-screenshot -d 5) &

The edited /etc/mdm/Init/Default file should look like this:

After that, just log out and wait for some seconds and you will have a screenshot of the login screen of Linux Mint 13. Just save the screenshot in whatever folder you want:

By the way, here is the new login screen of my Linux Mint 13 box, I just made it yesterday:

Note: This trick works in Linux Mint Cinnamon. However, due to the difference in application names between MATE and Cinnamon, you will need to replace "pluma" with "gedit" and "mate-screenshot" with "gnome-screenshot" to make this trick work in Cinnamon.